I replaced a front caliper last week after noticing it was moderately seized ('02 Acura RSX, 104K miles, daily and year-round driven in the salt/rust belt).

Today I decided to check my rotors after driving home from work. The rotor on the side of the new caliper was still significantly hotter than the rotor on the other side with the original un-serviced caliper.

Both sides have the same rotors and same pads. The brakes were bled after replacing the caliper.

Why would the side with the new caliper still be hotter than the side with the old caliper!

Bad proportioning valve? Old caliper not moving as freely as the new one and thus not being used as much?

Did you grease the caliper pins with silicone grease? Even though you bled the brakes, how long has it been since you changed the brake fluid?

On the newly remanned caliper?

No. Isn't that part of the reman process!

The mechanic said he bled the entire system, which I asked him to do. He only used one small container of brake fluid though. (I provided him with three.)

Not greasing the caliper pins with silicone grease is often why calipers hang up and generate tremendous heat. Naturally, this is not easy on pads or rotors.

This link may help:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-8.html#post1618425

An excellent product to have on hand is Motorcraft Silicone Brake Caliper Grease and Dielectric Compound (XG-3-A). It's available at your local Ford or Lincoln/Mercury dealer. It's amazing the number of applications this product can be used for; e.g. lubricating O-rings, rubber gaskets, disk brake caliper pins, plus using it as a dielectric compound for weatherizing battery and starter terminals and cables, fuse contacts, main grounds, main ECM ground, ECM connectors, igniters, coils, spark plug connectors, coating spark plug porcelein, and tail and brake lights.

Well, I'll check, but the (Honda, not A/M) remanned part was fully assembled (caliper installed on mounting bracket, the pins too of course) and the instructions said nothing about greasing the pins.

All Honda Service Manuals specify lubricating the caliper pins with silicone grease.

Your calipers are not floating on the pins but binding. This can be a MAJOR SAFETY HAZARD.

Well, of course, but who would assemble a caliper + bracket without greasing the pins!

Like I said, I'll check the pins and grease them if needed

By the way - I don't notice any braking issues while using the brakes like I did last week when the original caliper was hanging up

I could feel the drag from that old caliper.

Boots can also be binding or the pins can be worn. All of this is standard operating procedure for working on brakes.

Once again - this is a freshly remanned caliper, straight from the dealer!

The proportioning valve affects front to rear braking pressure.

Obviously, however, something is not right. Many people assume U-joints always come packed with EP grease. Sometimes they do but sometimes it's just packing grease to prevent rust. It needs to be purged, as bearing grease is pumped in. I learned a long time ago not to assume things. Personally, I would clean the pins with brake cleaner and grease them myself. Then, I know where I stand.

Are your new pads compounded the same as your old ones? Going from organic to semi-metallic can generate much more heat.